This invention relates to a control device for measuring the distance to a front going mobile body such as a motor vehicle and thereby controlling the speed of the mobile body on which it is installed such that a preliminarily specified distance can be maintained in between and more particularly to such a control device for controlling the starting motion of its own mobile body when the front going mobile body starts to move after stopping once.
The so-called adaptive cruise control (ACC) is becoming popular for moving bodies such as motor vehicles for measuring the distance to a front going vehicle by radar (whether of the optical or electromagnetic kind) and following it within a preliminarily determined maximum speed such that this separating distance can be maintained, depending on the speed. Vehicles with ACC are modernly coming to be provided with the function of stopping while maintaining a safe distance to the front going vehicle when the front going vehicle comes to stop.
From the point of view of automating the ACC, a further research is being continued for the technology of detecting the front going vehicle starting to move after once stopping and allowing its own vehicle to also start moving on the basis of the detected starting motion of the front going vehicle. If its own vehicle is allowed to start moving simply by detecting that the front going vehicle has started to move, however, an accident may result when a pedestrian or a bicyclist comes to enter the space in between while the vehicles are stopped. In view of such a possibility, Japanese Patent Publication Tokkai 2001-76299 discloses a technology of using a radar system to detect the presence of a pedestrian or a bicyclist between the front going vehicle and its own vehicle and to delay the starting motion of its own vehicle if the presence of a pedestrian or a bicyclist is thereby detected.
By a method of merely detecting an obstacle between the front going vehicle and its own vehicle by radar, however, there is still a possibility of a danger. FIG. 1 shows one's own vehicle 2 emitting a detection radar beam 3 towards a front going vehicle 1 to scan its front area but there is a so-called dead zone generated immediately in front. If a pedestrian 4 or a bicyclist enters this zone while the vehicles 1 and 2 are stopped, there is a possibility of failing to detect such an object within the dead zone. Moreover, since the diameter of the detection beam becomes smaller near its own vehicle 2, the reflected light from the object inside the dead zone becomes less likely to be detected reliably. If the object inside the dead zone is a bicycle and the detection beam 3 undergoes a specular reflection (or mirror reflection) by a flat metallic plate at its back, the reflected light is even less likely to be detected. In short, the attempt to detect an object between the two vehicles 1 and 2 by using radar is likely to fail, depending on the position and the condition of the object.